Field of the Invention
The present invention relates to dampers for use in clutches used for internal combustion engines for vehicles, mainly for saddle-riding type vehicles such as motorcycles, three-wheeled vehicles, and four-wheeled buggies.
Description of Related Art
As clutches for use in internal combustion engines of vehicles, it has been known that a damper for damping torque is interposed between a driving-side rotary member and a driven-side rotary member, and absorbs variation in torque that is generated in a power transmission system for an internal combustion engine (for example, JP Examined Utility Model Publication No. H03-002031). The damper disclosed in JP Examined Utility Model Publication No. H03-002031 is formed in a disk-like shape having, at the center portion thereof, a non-circular engagement hole with which an engagement projection of the driven-side rotary member engages, and a portion of the damper, on which torque acts, has the thickness increased in the circumferential direction. Further, cutout portions are formed on the inner side and the outer side, in the radial direction, of the portion (thickness-increased portion) having the thickness increased in the circumferential direction, thereby enabling the force that acts on the damper to be absorbed.
However, in the damper disclosed in JP Examined Utility Model Publication No. H03-002031, the thickness of the damper is minimal (narrowest) between the non-circular engagement hole and the outer circumference of the disk as viewed in the axial direction. When force acts on the damper, the thickness-increased portion is compressed to be greatly deformed. However, since a portion (narrowest portion) having the minimal thickness is formed on the side (front side) opposite to the side including a point of action on which force acts, the compressive force cannot be sufficiently absorbed at the narrowest portion, and a portion in front of the narrowest portion is less likely to be deformed. Therefore, force concentrates in a portion in the rear of the narrowest portion, and as a result, a crack may be generated in the damper.